1. Field of the Invention
The present invention relates generally to techniques for exposing or applying substrates of semiconductor device components to fluids and, more specifically, to methods in which fluid flows or is forced beyond a feature. In a particular example, the present invention relates to etch techniques and, more specifically, to etch methods in which an etchant flows or is forced beyond a feature while etching the feature. More particularly, the present invention relates to methods for forming vent holes of desired dimension in the bottom of so-called “blind ended” via holes. The present invention also relates to apparatus for causing an etchant to flow across a feature to be etched.
2. Background of Related Art
A variety of processes have been developed to form via holes through substrates, including semiconductor substrates, such as silicon wafers. Some via holes are formed so as to extend completely through a substrate, while others, which are referred to in the art as “blind ended” via holes, extend only partially through the substrate.
A blind ended via hole may be formed in the surface of a substrate by a variety of processes, including etch techniques that are timed in such a way as to permit the hole to extend only partially through the thickness of the substrate, which thickness may typically be about 700 μm to about 800 μm in the case of a full-thickness semiconductor wafer.
When blind ended via holes are formed in one surface of a substrate, a vent, which communicates with the via hole, may be formed in the other, opposite surface of the substrate. The presence of a vent facilitates the introduction of materials into and the formation of material layers within the relatively small (typically about 50 μm diameter) via hole. The size of the vent hole is typically small relative to (e.g., about one tenth of) the size of the blind ended via hole (e.g., about 5 μm diameter).
A vent may be formed by directing a laser beam of appropriate wavelength and intensity onto the surface of the substrate opposite the mouth of the via hole at a location that is in alignment with and, thus, opposite from its corresponding via hole. A focal point of the laser is positioned at a location just within the bottom of the via hole. Thus, the laser forms a vent that communicates with the other surface of the substrate, as well as a vent hole that establishes communication between the vent and the blind ended via hole.
Since a laser melts or ablates the material of the substrate, residual material may collect on the surfaces of a laser drilled features exposed to the heat of the laser (termed the “heat affected zone”), such as the vent or vent hole. This residual material is referred to as “slag.” Although the laser may form a vent hole with dimensions that are within reasonable tolerances, the size of the vent hole may be effectively reduced, or even closed, by the slag that results from use of a laser to faun the vent and vent hole. When slag-obstructed vent holes are undesirably small or occluded, material deposition may not proceed in a desirable fashion. As a consequence, the resulting via may include undesirable structural defects.
Neither conventional, relatively stagnant etching processes nor ashing effectively removes the slag.
Accordingly, there are needs for methods and apparatus for flowing or forcing etchants into or through small openings that extend substantially through a substrate to remove material from features by which the etchant passes.